Initiation of in situ combustion



United States Patent 3,314,476 INITIATION OF IN SITU COMBUSTION DallasR. Staples, Houston, and Joseph C. Allen, Bellaire, Tex., assignors toTexaco Inc., New York, N.Y., a corporation of Delaware N Drawing. FiledDec. 26, 1963, Ser. No. 333,704 Claims. (Cl. 16632) This inventionrelates generally to the treatment of underground formations whichproduce petroleum. More particularly, this invention relates to thecarrying out of an in situ combustion operation within a permeableunderground formation. In accordance with one embodiment, the practiceof this invention is directed to a method of initiating in situcombustion within a permeable underground formation, e.g., by initiatingin situ combustion within a petroleum bearing underground formation bythe use of spontaneous ignition agents.

Various techniques have been practiced for the secondary recovery ofpetroleum from underground formations, including thermal recoverymethods, such as in situ combustion, which employ at least one injectionwell and at least one production well.

In a conventional in situ combustion operation, ignition of the oil inplace in the formation may be effected by any one of several well knownmethods. One such method involves heating the petroleum bearingformation to a sufiieiently high ignition temperature as by means of adownhole electrical heater. A combustion-supporting gas, such as air oroxygen-enriched air, is then introduced into the formation by way of thewell bore. A high temperature zone or combustion front with temperaturesin the range 7002500 F., is created by the reaction between thethus-introduced oxygen and the combustible petroleum residues within theformation, such as combustible residues resulting from the distillationand/or thermal cracking of the petroleum orginally in place orintroduced thereinto. As the operation proceeds, the combustion frontmoves outwardly from the well bore into the formation in the directionof flow of hot gaseous combustion products.

As a result of combustion of the in-place oil gaseous materials aregenerated which consist of the gaseous products of combustion andvolatized components of the hydrocarbons present. These hot gases moveoutwardly into the formation and lose heat to the formation. Thus, asmore oxygen-containing gas is supplied through the well bore, the hightemperature combustion front moves outward from the well bore withoutfurther direct application of heat to the area immediately surroundingthe well bore. The distance the combustion front moves outwardly, andaccordingly, the volume of the petroleum producing formation swept bythe combustion process, is dependent upon the relative magnitude of therate of heat generation (due to the combustion of combustible residues)and the rate of heat loss to the surrounding formation. Although theexact mechanism of an in situ combustion is not known definitely, thefollowing sequences of events is postulated and is presented herein forthe purpose of enabling one skilled in the art to understand thepractice of this invention.

As the combustion front approaches a given volume of thepetroleum-containing formation, the temperature of this volume offormation increases. This results in a reduction in the viscosity of theformation liquids therein due to their temperature rise. These fluidsthen may be moved more readily under the influence of the hot gas streamcontinuously emanating from the combustion. As the temperature of thisvolume of formation continues to rise, distillation of the liquidstherein begins. The products of the distillation condense in the coolerregions of the formations outward from the high temperature combus-tionfront in the direction of gas flow. The distillation continues as thetemperature rises until the heavier components remaining within thepetroleum originally in place Within the formation or introducedthereinto prior to effecting in situ combustion begin to crack orotherwise thermally decompose, yielding hydrocarbon gases, coke andsolid carbonaceous residues. As the temperature continues to rise, apoint is reached at which the hot coke or hot combustible residues willbegin to combine chemically with the oxygen with the resulting releaseof heat to the formation and the gas stream emanating therefrom. Thisheat is carried away by the outwardly moving gas stream and also to alimited extent is transferred to the adjacent regions of the formationby conduction. When the coke and combustible residues have been burnedaway, there remains a volume of substantially liquid-free formationwhich, unless otherwise treated, is cooled gradually by the oncomingrelatively cool combustion-supporting gas or air entering thethus-treated given volume of the formation via the well bore.

One difficulty in carrying out an in situ combustion recovery operationinvolves the operation of initiating combustion in the formation.Various methods have been proposed heretofore for underground initiationof combustion. For example, electrical heating devices or gas firedbottom hole igniters or heaters suitable for lowering within theborehole opposite the formation wherein the combustion is to beinitiated, have been suggested. Another method involves the introductionof phosphorus into the petroleum producing formation.

Still another method of the prior art, described in copcndingapplication Ser. No. 215,459 filed on Aug. 7, 1962, in the names ofValery N. Bednarski, Robert E. Kunetka and Joseph C. Allen, and now U.S.Patent No. 3,180,412, involves introducing into the petroleum-bearingformation to be ignited an ignition agent comprising an unsaturatedaliphatic compound comprising only carbon, hydrogen and oxygen atoms andcontaining at least 16 carbon atoms per molecule, particularly a dryingoil or semi-drying oil, and then passing into the same formation a gascomprising free oxygen to effect spontaneous .eombustion of thealiphatic compound with resulting ignition of the petroleum. Anoxidation promoter, for example, an organic nitrogen base such aspyridine may be included in the ignition mixture to promote thespontaneous ignition reaction. Also, oxidation catalysts or dryers, suchas cob-alt naphthenate have been included to promote spontaneouscombustion. Powdered magnesium can also be used to increase the amountof heat released after spontaneous combustion has been initiated.

The above method has been satisfactory in many tests, but it has beenfound that it sometimes fails in injection wells wherein it is notpossible to maintain high air pressures, such as more than psi, becauseof excessive permeability or fracturing in the pay formation adjacentthe injection well.

It is an object of this invention to provide an improved method forinitiating in situ combustion within a permeable petroleum-bearingformation.

A further object of the invention is to provide a thixotropiccomposition which, when placed in a permeable formation, will set up asa gel to yield conditions favorable to initiation of combustion in theformation.

In accordance with this invention, it has been discovered that theinitiation of in situ combustion of the hydrocarbons contained in apetroleum bearing underground formation may be facilitated byintroducing a combus- '2 a ously combustible material into the formationand then passing an oxygen-containing fluid therethrough, ignition maybe enhanced and facilitated by introducing a combustible thixotropicsubstance into the formation prior to the introduction of thespontaneously combustible material.

It has further been found that a desirable thixotropic substance may beprepared by incorporating a saponifiable organic compound containing atleast l6 carbon atoms per molecule and an alkali metal hydroxide with apetroleum derived material such as crude oil in such proportions thatthe mixture will set up as a gel when agitation is ceased.

Improved results can be obtained by preceding and following theinjection of the thixotropic substance into the formation with theinjection of crude oil or other combustible petroleum derived materialsprior to the injection of the spontaneous ignition chemical.

Under some conditions spontaneous ignition can be obtained by thepassage of air or oxygen-enriched air through a gelling substanceprepared with an unsaturated saponifiable aliphatic compound, withoutthe subsequent injection of a spontaneously combustible material intothe petroleum bearing formation.

in practicing the method of this invention, the desired number ofwellsis drilled into the formation, a minimum of two boreholes or wellsusually being required, one of these being called an input or injectionwell, the other and output or production well. It is to be understoodthat there may be more than one well of each type if so desired. Theinput well provides access for ignition of the combustion reaction, andfor injecting a combustion supporting gas or fluid into the formation.The output well, onthe other hand, serves primarily for collection ofthe oil being produced and the gaseous products of combustion, and alsoserves as a means for bringing such oil and combustion products to thesurface.

It is a usual practice when an underground in situ combustion operationis contemplated to first establish a path or zone of permeabilitythrough the petroleum containing formation, extending from an injectionwell to a production well or wells. In order to establish such apermeable path, a gas, usually air although an inert gas such asnitrogen may be used if so desired, is pumped into the input well undersutficient pressure until it has been determined that a permeable pathexists between the injection well and the output well or wells. If airpressure alone is not sufficient to achieve the desired degree ofpermeability, it is sometimes necessary to employ hydraulic fracturingat the input well to accomplish the desired result.

Ordinarily, once permeability has been established through thepetroleum-containing formation, it is possible to initiate in situcombustion in accordance with one of the methods of the prior art.However, we have found that in many instances it is difficult toinitiate combustion due to physical conditions within the formationwhich result in relatively low pressures in the zone where ignition iscontemplated. These physical conditions may be excessivepermeability-either natural or due to excessive hydraulic fracturing ofthe petroleum reservoir and so forth. We have found in general that inorder to initiate combustion in the formation adjacent the input wellthat the pressure in this zone must be at least 150 p.s.i.g., andpreferably above 200 p.s.i.g., when the combustion supporting gas isinitially passed through the formation at the desired rate of gas flow.Accordingly, the method .of this invention is particularly useful whenit is desired to carry out an in situ combustion operation for therecovery of petroleum from an underground formation wherein the pressuredrop of the combustion supporting gas through the petroleum-bearingformation between the injection or input well and the production oroutput well is too low to maintain sufficient pressure at the input wellto initiate combustion. The method may be employed advantageously withany of the ignition methods of the prior art, such as by means ofdown-hole heater, surface preheating of the injected combustionsupporting fluid, and particularly by means of spontaneously combustibleignition materials.

It has been determined experimentally under well igni tion conditionsthat the pressure on a spontaneously combustible chemical, such as afatty oil, placed in a well formation and exposed to anoxygen-containing gas, as in the initiation of in situ combustion by themethod of copending application Ser. No. 215,459 referred tohereinbefore has a marked effect on the success with which spontaneouslycombustible material may be ignited by a combustion supporting gas. Ingeneral, moreover, when using the socalled chemical igniters, such aslinseed oil fatty acids and similar materials, the induction timerequired for spontaneous ignition is reduced as the pressure isincreased. It has been further ascertained that the shorter theinduction time or in other words the shorter the length of time it isnecessary to pass oxygen-containing gas through the combustible liquidbefore ignition takes place spontaneously, the higher are thetemperatures reached upon spontaneous ignition for a combustible liquidof fixed B.t.u. content. It has also been demonstrated that the higherthis ignition temperature, the better chance there is for successfulignition of the inplace crude. Through this relationship successfulignition of the crude is to a large degree dependent upon pressuremaintained on the combustion liquid.

In wells in which ignition has been unsuccessful due to insufficientpressure in the input well, the principles of the present invention havebeen used successfully by forcing the thixotropio hydrocarbon gel intothe injection well and then into the excessively permeable portion ofthe formation surrounding the borehole where its physical state changesfrom that of a pumpable liquid to a solid or semisolid gel, whichresults in sufficient blocking of the permeable path to enable attainingthe required pressure at the input well. In a preferred embodiment, aVolume of petroleum derived from the formation by ordinary productionpractices, called lease crude, is first forced into the input well andthe formations adjacent the input well. The lease crude is then followedby injection of the hydrocarbon gel of the present invention into theinput well and the surrounding permeable formation. In the eventchemical ignition is employed, the gel is then followed by injection ofa chemical which ignites spontaneously when a combustion supporting gassuch as air is passed therethrough. Preferably a volume of lease crudeis injected.

into the formation between the hydrocarbon gel and the chemical igniterin the event any excess caustic in the gel may tend to act as a catalystpoison and interfere in any way with the spontaneous combustionproperties of the chemical igniter.

Following the placement of the hydrocarbon gel and the chemical igniterin the petroleum containing formations adjacent the input well, acombustion-supporting oxygen-containing gas, such as air oroxygen-enriched air or substantially pure oxygen, is introduced into theformation via the input well. Air preheated to above F. and preferablyabove 200 F. is particularly suitable. If a downhole heater is used forinitiating ignition, the procedure is the same except that the injectionof the chemical igniter is omitted.

Reaction of the oxygen content of the combustion supporting gas with thechemical igniter causes ignition of the igniter by means of spontaneouscombustion. The heat thus produced raises the temperature of theformation such that ignition of the petroleum content, including thethixotropic gel, occurs. Continued injection of combustion supportinggas into the input well results in the establishment of a combustionzone or reaction front which moves progressively away from the inputwell by the burning of combustible material contained in the pores ofthe formation.

The aforesaid hydrocarbon gel is prepared at the surface by mixing crudeoil or other petroleum derived liquid hydrocarbon with from 1.5 to 3.0percent by weight of a saponifiable organic compound of a type to bedescribed hereinafte-r and with sufficient caustic or alkali forneutralization of the acidic groups of the organic compound, ordinarilyin the range of from 0.4 to 0.9 percent by weight. Mixing is notcritical and may be carried out in conventional pump and tank typemixing units available to oil well drilling operators. If a catalyst orpromoter is to be included in the gel composition, it ordinarily isadded to the organic compound prior to mixing with the hydrocarbon.Although the proportions used will vary somewhat with the type ofhydrocarbon or crude oil used, as well as with the particular organiccompound employed, it has been found that a composition comprising about2.0% of fatty acid and about 0.6% caustic soda by weight, the remainderbeing crude oil, yields a satisfactory thixotropic substance which is agel under static conditions, but which becomes fluid when pumped orcirculated. It is desirable that once the mixture has been compounded,it should not be allowed to stand in the mixing equipment prior topumping it down the Well bore.

It further has been found that an unsaturated oxygenated aliphaticorganic compound, such as an unsaturated long chain fatty acid, fat orfatty oil, and the glycerides and esters of unsaturated long chain fattyacids, including esters formed with unsaturated long chain fattyalcohols, are particularly suitable for use as the saponifiable organiccompound in that the unsaturated linkages are subject to auto-oxidationunder the conditions existing in the well bore when an oxygen-containinggas is passed into the permeable formation containing the hydrocarbongel.

Exemplary unsaturated aliphatic organic compounds which are suitablyemployed in the practice of this invention include the followingmonocarboxylic acids, as well as their isomers and the glycerides andesters thereof, for example: monoethylenic types such as oleic,palmitoleic, phytenic and erucic; diethylenic types such as linoleic anddodecadienoic, triethylenic types such as linolenic; acetylenic typessuch as stearolic and eicosynoic; and hydroxy unsaturated types such asricinoleic.

It has been found that the related saturated ali hatic organic compoundsalso are useful in carrying out the invention in that they are capableof producing hydrocarbon gels when mixed with oil and an alkali metalhydroxide. Examples of such saturated aliphatic organic compoundsinclude the following monocarboxylic acids as well as their isomers andthe corresponding alcohols and esters thereof: palmitic, margaric,stearic, arachidic and behenic. Hydroxy saturated acids includedihydroxystearic, dihydroxybehenic and tetrahydroxystearic or sativicacid.

Also encompassed by the invention are the natural processed fats andfatty oils containing one or more of the foregoing types of aliphaticorganic compounds and more particularly the so-called drying oils andsemi-drying oils. Suitable saponifiable nonhydrocarbon oils, vegetableand animal (mammal or fish), or mixtures thereof, which may be employedinclude corn oil, cottonseed oil, sesame seed oil, sunflower seed oil,soybean oil, poppyseed oil, perilla oil, tung oil, citicica oil, linseedoil, and fish oils, such as herring oil, sardine oil, menhaden oil,whale oil, seal oi'l, porpoise oil, dolphin oil, and the like. Ingeneral, any saponifiable nonhydrocarbon oil, animal or vegetablecapable of producing thixotropic gel in accordance with the inventionmay be used. However, an unsaturated animal or vegetable oil ispreferred. For the most part, these oils, such as linseed oil and thelike, comprise triglycerides of unsaturated long chain fattymonocarboxylic acids.

It is also contemplated that gels formed by incorporating other types ofemulsifying agents, such as aromatic sulfonates, also may be employed.

Desirably and in accordance with one embodiment of this invention, thereis admixed with the hydrocarbon gel, preferably by mixing with thehydro-carbon oil, the saponifiable organic compound or the alkali metalhydroxide prior to gellation, and prior to introduction into thepermeable formation undergoing treatment a suitable oxidation promoter.Organic nitrogen bases, such as pyridine, pyrrole, piperidine, anilineand dimethylaniline, are particularly useful as oxidation promoters topromote a spontaneous in situ combustion reaction in accordance withthis invention.

In accordance with another embodiment of the invention, and particularlywhen the hydrocarbon gel comprises an unsaturated saponifiable organiccompound, the gel also contains admixed therewith a minor amount ofdrying oil oxidation catalyst or dryer, such as cobalt naphthenate,cobalt tallate, cobalt octoate, and similar iron, manganese or leaddryers in order to catalyze oxida tion thereof.

In accordance with still another embodiment of the invention, there isincorporated into the gel a suitable minor amount, in the range of0.2510% by weight, of finely-divided, powdered magnesium or magnesiumdust. Once spontaneous in situ combustion has been initiated, thepowdered magnesium greatly increases the amount of heat released and thetemperature generated during initiation of the in situ combustionprocess within the formation undergoing treatment.

The chemical igniter may be any of the several types disclosed in theprior art. However, it has been found that the materials disclosed incopending application Ser. No. 215,459 are particularly suitable for usein accordance with the present invention. Such igniters consist ofmaterials characterized generally as an oxygenated aliphatic organiccompound, such as an unsaturated long chain fatty acid or an unsaturatedlong chain fatty alcohol or fat or oil, and the glycerides ofunsaturated long chain fatty acids, and more particularlyunsaturated-aliphatic compounds comprising only carbon, hydrogen,andvoxy gen atoms and containing at least 16 carbon atoms per molecule.Particularly useful are the unsaturated nonhydrocarbon oils,particularly those oils, so-called drying oils or so-called semidryingoils having an iodine number greater than 100, especially greater than130. Desirably, there may be admixed with the nonhydrocarbon oil asuitable oxidation promoter, of which the organic nitrogen bases such aspyridine, dimethylaniline and the like are particularly useful.Desirably also, the unsaturated nonhydrocarbon oil or unsaturatedaliphatic compound may also contain admixed therewith an oxidationcatalyst ordryer, such as cobalt naphthenate, cobalt tallate, cobaltoctoate, and similar iron or lead driers. As still another ingredient asuitable amount of powdered magnesium or magnesium dust also may beincorporated to provide a source of intense heat upon ignition of thechemical igniter.

The following is an example of the process of this invention forinitiating an in situ combustion as performed in an oil well in the GulfCoast area of the United States.

Example Injection and production wells were drilled in preparation of anin sit-u combustion production program of an oil field in the southernportion of Texas in which primary production has been depleted. A lineof injection wells were drilled across the width of the field andproducing wells were drilled to strike on each side of the injectionline.

In 65% of the injection wells in the field, ignition was accomplishedwithout difficulty either by the injection of ignition chemicals inaccordance with the method of copending application Ser. No. 215,459, orby means of an electrical heater for heating the face of the oil-bearingsection in accordance with well known production practice. The ignitionchemicals consisted of two drums of water-white distilled linseed oilfatty acids containing approximately one pound of cobalt naphthenate andone pound of dimethylaniline per hundred pounds of the fatty acids. Thechemicals were introduced into the well bore and then forced into theformation by injection of nitrogen. Air injection was commenced at arelatively low rate of a few thousand cubic feet per hour at a maximuminjection pressure in the neighborhood of 300 lbs. per square inch andwas continued at the low rate for about 12 to 14 hours, after which timethe rate was increased to the combustion injection rate of about 1million cubic feet per day. Approximately one-half hour to 1 hour afterthe increase in air injection rate the temperature began to rise rapidlyas a result of initiation of combustion.

It was found, however, that 35% of the injection wells could not beignited by the procedure em loyed. Analysis of the conditions existingin the wells which did ignite and those which did not revealed thatthose wells which could not be ignited by the usual procedures had a common property in that the air pressure in the well bore during theignition attempts could not be raised above 150 lbs. per square inch,whereas in the ignited wells the air pressure rose above 150 p.s.i.g.

The following is a description of the well completion procedure for onewell in the field, a description of the unsuccessful attempt to ignitethis well, and a description of the application of the present inventionwhich resulted in successful ignition of the petroleum in the formationadjacent this well.

The well was prepared for ignition by drilling to a total of the holewith slotted casing being used opposite the pay depth of about 200 feet,or about 25 feet below the bottom of the pay zone. Casing was then runto the bottom zone. The casing was then cemented from the top of the payzone to the surface. After this the Well was cleaned out to total depth.A string of tubing was run into the hole with the bottom of the tubingopposite the bottom of the pay zone.

After an air injectivity test to determine that the well would acceptair at the desired injection rate, the well was purged with two casingvolumes of gaseous nitrogen injected at the well head assembly. Twodrums, or 110 gallons, of ignition chemicals were then displaced intothe well with nitrogen from a displacement vessel located at thesurface. Additional nitrogen was injected to force the ignitionchemicals into the formation and to purge the borehole, as well as toestablish receptivity of the nitrogen to the formation at a decreasingpressure gradient. Injection of air for initiation of combustion wasthen started at an injection rate of 150,000 cubic feet per day for thefirst eight hours, after which the injection rate was raised to 210,000cubic feet per day for another eight hours. After this, the rate wasincreased to 700,000 cubic feet per day for a two-hour period. Nocombustion of the ignition chemical was obtained and combustion of thein-place oil was not achieved.

The ignition chemicals employed in the foregoing ignition attemptconsisted of water-white distilled linseed oil fatty acids containingone pound of cobalt naphthenate as an oxidation catalyst and one poundof dimethylaniline as an oxidation promoter per 100 pounds of fattyacids. This was approximately equivalent to onehalf gallon of each ofthese materials per 55 gallon drums of the fatty acids.

Following the unsuccessful attempts to obtain ignition in this andseveral other wells in the field, a study of the conditions in the wellswhich did not ignite and the other wells in which ignition was obtainedby chemical ignition employing the same operating procedure revealedthat following the injection of the ignition chemicals the well borepressures during the injection of air were noticeably lower for thewells that did not ignite than for the wells in which ignition wasachieved. It was found the well head pressures during this period weregenerally above 235 pounds per square inch in the wells in whichignition was achieved and below about 200 p.s.i. in the wells whichfailed to ignite.

In a further attempt to initiate combustion in the well of this example,the following procedure was employed. First, five barrels of leasecrude, crude previously obtained by production from the field, werepumped into the well and forced into the pay zone by means of gaseousnitrogen. This was followed by the injection of fifteen barrels ofgelled oil followed by injection of another five barrels of lease crude.

The gelled oil was prepared at the surface by mixing lease crude with2.0 percent by weight of linseed oil fatty acids and 0.6 percent byweight of caustic soda in a continuous blender or proportioning deviceat ambient temperature. The output from the blender was connecteddirectly to the surface injection pump in order that thecrude-fatty-acid-caustic mixture not be allowed to stand quiescent asunder static conditions this composition sets up into a gel. Thecomposition of a suitable gelled oil may vary slightly depending on thecrude or other oil used and upon the degree of gelling desired. However,the composition ordinarily will not vary greatly from that given above,namely 2.0% by weight fatty acids and 0.6% by weight caustic soda. Ithas been found that crudes containing in excess of about one percentwater or those containing a high concentration of demulsifier, as from adesalting, deernulsifier, or dehydration operation, will not form a gelunder static or quiescent conditions.

Following the second injection of lease crude, a short air injectivitytest was made to ascertain the receptivity of the formation to air. Thecasing and tubing were then purged with gaseous nitrogen and the casingclosed off at the surface. Three barrels of ignition chemicals of thesame composition as previously used were injected into the tubing. Thesechemicals were comprised of water white distilled linseed oil fattyacids containing one pound of cobalt naphthenate and one pound ofdimethylaniline per pounds of fatty acids. The ignition chemicals wereforced into the formation by means of nitrogen injected down the tubing,following which air injection was started into the tubing at a rate of180,000 cubic feet per day. As evidenced by both a pressure surge in theborehole and by an increase in borehole temperature in the vicinity ofthe pay zone, ignition was successfully achieved after an air injectionperiod of about one hour. A pressure surge of 80 p.s.i. occurred uponignition, which was considerably higher than the pressure surges notedin wells successfully ignited without the use of gelled oil. In thoseinstances a pressure surge of from 20 to 30 p.s.i. was noted in severalwells and in other instances the wells were ignited with only a slightlypressure surges of less than 10 p.s.i. In addition, in the example wellusing the gelled oil, a secondary pressure surge was noted after anadditional 10-20 minutes of air injection, thereby indicating thatanother interval of the formation had ignited. Temperatures in the lowerend of the tubing fluctuated wildly, going as high as 1100 F. Thepressure after about two hours did not decline to the original pressureas had been the case in all of the previously ignited wells. Instead thepressure after about 5.4 hours was still p.s.i. or 20 p.s.i. higher thanthe initial pressure. This is another indication that the procedure ofthe present invention achieved more efficient ignition by igniting moreof the pay section. This was in a well which previously did not respondto ignition by the method of the prior art.

Although the invention has been described as employing a spontaneouslycombustible ignition chemical following the injection of the gelled oil,it is contemplated that ignition may be initiated by means of a downhole heater or one of the other ignition methods of the prior art. It isfurther contemplated that an unsaturated fatty acid may be employed asthe saponifiable constituent of the gelled oil mixture with the gelledoil itself acting as an ignition chemical by spontaneous initiatingcombuston upon the injection of air, particularly when there areincorporated therein oxidation catalysts and promoters of the typesdescribed hereinbefore.

For the ignition of formations characterized by either highly permeablestreaks or by fractures it is further contemplated that lease crude orheavy oil and caustic may be mixed with the unsaturated fatty oilignition chemical containing an oxidation catalyst and/or promoter toachieve ignition by reducing the permeability of these larger passagesthrough the formation being produced.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made Without departing from the spirit andscope thereof and therefore only such limitations should be imposed asare indicated in the appended claims.

We claim:

1. In the method of initiating in situ combustion in a permeablepetroleum bearing underground formation traversed by a borehole whereincombustion of the petroleum in the formation is initiated by placing aspontaneously combustible material in the formation and passing anoxygen-containing gas therethrough, the improvement comprising theintroduction into said formation prior to the introduction of saidspontaneously combustible material of a gelling composition comprising aspontaneous 1y oxidizable saponifiable constituent and having theproperty of being relatively fluid under dynamic conditions and ofsetting to a gel under static conditions.

2. In the method of claim 1, said gelling composition comprising apetroleum material, a spontaneously oxidizable saponifiable organiccompound containing at least 16 carbon atoms per molecule and an alkalimetal hydroxide.

3. In the method of claim 2, said spontaneously oxidizable saponifiableorganic compound being an unsaturated long chain fatty acid.

4. In the method of claim 3, said unsaturated long chain fatty acidcomprising fatty acids derived from linseed oil.

5. In the method of claim 2, said spontaneously oxidizable saponifiableorganic compound being a glyceride of an unsaturated long chain fattyacid.

6. In the method of claim 2, said alkali metal hydroxide being sodiumhydroxide.

7. In the method of claim 2, said spontaneously oxidizable saponifiableorganic compound being present in an amount of approximately one and one'half to three percent by weight of said gelling substance and saidalkali metal hydroxide being present in an amount of approximatelyfour-tenths to nine-tenths percent by weight of said gelling substance.

8. The method of initiating in situ combustion within a permeablepetroleum bearing underground formation penetrated by at least aninjection well comprising the forming of a zone of permeability in saidunderground formation by flowing air therethrough, purging saidinjection well by an inert gas, introducing into said formation a firstamount of crude petroleum, introducing into said formation a combustiblegelling composition having the property of being relatively fluid underdynamic conditions and of setting to a gel under static conditions,introducing into said formation a second amount of crude petroleum,introducing into said formation by displacement: with an inert gas anamount of a spontaneously combustible liquid mixture comprising anunsaturated aliphatic organic compound containing at least 16 carbonatoms per molecule together with an oxidation catalyst and an oxidationpromoter, subsequently introducing through said injection Well into saidformation a gaseous stream containing free oxygen for a period of timesuflicient to increase the temperature of the treated formation byoxidation of said organic compound therein for ignition of the petroleumin said formation and flowing air through said formation for in situcombustion therein.

9. In the method of initiating in situ combustion in a permeableunderground formation traversed by a borehole wherein combustion of thepetroleum in the formation is initiated by placing a spontaneouslycombustible material in the formation and passing a combustionsupporting gas therethrough, the improvement wherein said spontaneouslycombustible material is in the form of a thixotropic compositioncomprising crude petroleum, a spontaneously oxidizable saponifiableorganic compound containing at least 16 carbon atoms per molecule and analkali metal hydroxide.

10. In the method of claim 9, said thixotropic composition comprisingcrude petroleum, a spontaneously oxidizable saponifiable organiccompound containing at least 16 carbon atoms per molecule, an alkalimetal hydroxide and a minor proportion of an organic nitrogen base.

11. In the method of claim 9, said thixotropic composition comprisingcrude petroleum, a spontaneously oxidizable saponifiable organiccompound containing at least 16 carbon atoms per molecule, an alkalimetal hydroxide and a minor proportion of a drying oil oxidationcatalyst.

12. In the method of claim 9, said thixotropic composition comprisingcrude petroleum, a spontaneously oxidizable saponifiable organiccompound containing at least 16 carbon atoms per molecule, an alkalimetal hydroxide, a minor proportion of a drying oil oxidation catalystand a minor proportion of powdered magnesium.

13. In the method of initiating in situ combustion in a permeablepetroleum bearing underground formation traversed by a borehole whereina combustion supporting gas is passed down the borehole and into theformation during the ignition procedure, the improvement comprisingreducing the permeability of said formation prior to introducing saidcombustion supporting gas by introducing into said formation acombustible thixotropic materal which partially blocks the permeablepassages and maintaining said reduced permeability until ignition hasbeen effected.

14. The method of claim 13 wherein said combustion supporting gas issupplied to said formation during the initiation of combustion at aborehole pressure in excess of pounds per square inch.

15. In the method of initiating in situ combustion in a permeablepetroleum bearing underground formation, traversed by a borehole theimprovement comprising preparing a combustible thixotropic fluid mixtureat the surface of the earth in the vicinity of said borehole,continuously mixing said prepared mixture until pumped down saidborehole and into said formation, pumping said mixture down sad boreholeand into said formation, stopping said pumping when said mixture is inplace in said formation thereby allowing said mixture to set up as a gelwith resulting partial plugging of said formation prior to and duringinitiation of combustion.

References Cited by the Examiner UNITED STATES PATENTS 2,863,510 12/1958Tadema et al. 166-38 2,880,802 4/1959 Carpenter 16611 3,072,190 1/ 1963Reichle 16639 3,180,412 4/1965 Bednarski et a1 166-11 3,198,249 8/1965Willman 166-11 X 3,261,400 7/1966 Elfrink 16630 OTHER REFERENCES Rogers:Composition and Properties of Oil Well Drilling Fluids, 1st edition,Gulf Publishing Co., Houston, Texas, 1948, pp. 422 to 432 relied on.

JACOB L. NACKENOFF, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

S. J. NOVOSAD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,314,476 April 18, 1967 Dallas R. Staples et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below Column 7, line 32, strike out "of the hole with slottedcasing being used opposite the pay" and insert the same after "bottom"in line 34, same column 7 column 8, line 52, for "slightly" read slightcolumn 10, line 51, for "sad" read said Signed and sealed this 7th dayof November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. IN THE METHOD OF INITIATING IN SITU COMBUSTION IN A PERMEABLEPETROLEUM BEARING UNDERGROUND FORMATION TRAVERSED BY A BOREHOLE WHEREINCOMBUSTION OF THE PETROLEUM IN THE FORMATION IS INITIATED BY PLACING ASPONTANEOUSLY COMBUSTIBLE MATERIAL IN THE FORMATION AND PASSING ANOXYGEN-CONTAINING GAS THERETHROUGH, THE IMPROVEMENT COMPRISING THEINTRODUCTION INTO SAID FORMATION PRIOR TO THE INTRODUCTION OF SAIDSPONTANEOUSLY COMBUSTIBLE MATERIAL OF A GELLING COMPOSITION COMPRISING ASPONTANEOUSLY OXIDIZABLE SAPONIFIABLE CONSTITUENT AND HAVING THEPROPERTY OF BEING RELATIVELY FLUID UNDER DYNAMIC CONDITIONS AND OFSETTING TO A GEL UNDER STATIC CONDITIONS.